High pressure chrome refractory



Feb. 26, 1935. R. P. HEUER 1,992,433

v HIGH PRESSURE CHRQIE REFRACTORY Filed. Feb. 15, 1933 Patented Feb. 26,1935 UNITE PATEN FFICE Russell Pearce Heuer, Bryn Mawr, Pa., assignor toGeneral Refractories Company, a corporation of Pennsylvania ApplicationFebruary 15, 1933, Serial No. 656,938

18 Claims.

My invention relates to the manufacture of chrome refractory brick. Thisapplication is a continuation in part of my application Serial No.323,890, filed December 5, 1928 for Dense mix for refractory bricks.

A purpose of my invention is to make chrome brick of greater density andless porosity for use without previous firing, by methods which arebetter and more economical, using a mix of definite proportions oflarger and smaller graded sizes of non-plastic chrome particles,suitably bonding the non-plastic mix, and subjecting the non-plastic mixto high pressure to cause tight interfitting of the particles. In thisway the voids are decreased to a minimum, the need for bonding materialis reduced, and the chrome brick are enabled to give improved serviceand to withstand high temperatures in a better manner.

A further purpose is to employ between 45% and 65% (preferably 55%) oflarger non-plastic chrome particles between 10 and mesh per linear inchand between 55% and (preferably of smaller non-plastic chrome particlesthrough mesh per linear inch (preferably 25 through or mesh per linearinch) in chrome brick, desirably regrinding the intermediate particlesbetween 30 and 50 mesh per linear inch to make smaller particles, and tosubject the mixture, without plastic material or fluxing ingredients, topressure in excess of 1000 pounds per square inch.

A further purpose is to operate a crushing, grinding and screening millon a cycle that adapts the mill to deliver ground chrome ore in the formof larger and smaller grain sizes in predetermined relative quantitieswithout the presence of grains of an intermediate size, the relativequantities of larger and smaller size particles be,- ing preferablyabout 55% and 45% respectively. A further purpose is to grind arefractory (preferably chrome ore) under conditions producing a relativeexcess of larger particles for the intended use, thus insuring thatsuflicient larger particles are obtained, and to subsequently regrindthe excess of larger particles.

A furtherpurpose is to employ magnesia in a chrome brick made inaccordance with my invention.

Further-purposes appear in the specification and in the claims.

My invention relates to the methods involved and to the productsobtained.

Figure 1 is a ternary diagram for different mixes that may be made fromthree different graded sizes of nonlastic chrome particles mixedtogether in different proportions, and is given to indicate the resultsof research work that I have done to determine the way in which thedensity of chrome mixes is dependent upon the relative quantities ofthree different graded sizes of particles in the mix.

Figure 2 is a diagrammatic view showing my. method of operating acrushing, grinding and screening mill for the preparation of a chromebrick mix in accord with my invention.

Figures 3, 4 and 5 are diagrammatic fragmentary sections throughdifferent hypothetical mixes for forming chrome brick, Figure 3illustrating a mix made up exclusively of larger or A particles, Figure4 illustrating a mix of larger or A, smaller or C, and intermediate or Bsizes, and Figure 5 a mix made up of larger or A and smaller or Cgrains, but without grains of intermediate or B size.

In the drawing like numerals refer to like parts.

Many non-plastic refractory materials may be used to produce brick ofhigh density'by grading the particles into larger and smaller sizes,with the. partial or complete elimination of intermediate sizes, andcombining the larger and smaller sizes in definite proportions. This hasbeen explained by me in my U. S. Patent No. 1,851,181, granted March 9.1932. Prior to the invention of the said patent, it was common practiceto form brick from ground refractory which passes a specific size ofscreen and which therefore comprises indiscriminately different sizes ofparticles, all of which however are sufiiciently small to pass thescreen used.

However, by eliminating intermediate size particles and combining thelarger and smaller sizes as discussed in my Patent No. 1,851,181, I havefound that the service characteristics, such as Y strength, resistance-to abrasion and spalling, and resistance to molten slags, hot metals,and hot products of combustion of refractory brick are much improved.This improvement I attribute largely to increased density andcorrespondingly decreased void space obtained by the proper grading ofthe sizes of the particles and combining of the graded sizes.

Chrome ore is an excellent example of a nonplastic material which may bemade into greatly improved brick by proper grading and combining of theparticle sizes. More benefit of my invention is obtained with chromebrick than with many refractories, because of the closeness with whichchrome brick follow the law which I have diswvered. I find that, themore dense the re- -.fractory mix from which chrome brick are formed,the more dense will be the brick, and

that by suitably proportioning the relative quantitles of the particlesof diiferent graded sizes that together make up the mix. I am able tomaterially increase the density of the mix from which the chrome brickare subsequently formed, with a corresponding increase in density andgreat improvement in the service characteristics of the chrome brick.

The increase in density of the mix is incident to a decrease in the voidspace between the mix particles, which, in turn, is doubtless due to abetter interfitting of the brick particles with one another, the moreperfect interfitting of the particles making the tighter, denserstructure that gives the greatly superior service characteristics. Sincemy chrome particles are non-plastic, it will be evident that they do nothave associated with them during forming the considerable film ofmoisture which surrounds plastic particles. There is therefore not anysubstantial loss in tightness of interfitting, or increase in voidspace, due to the driving air of moisture by heating operations whichtake place subsequent to interfitting, such as drying, firing, orsubjecting to firing temperature during use in a furnace lining.Likewise, since my chrome brick do not contain suflicient fluxes orsimilar materials to promote plastic flow at high temperatures, such asthe temperatures of use in a metallurgical furnace in which chrome brickare employed, there is no tendency of the particles to fiux togetherinto a solid mass and destroy the interfitting of the particles,producing a shrunken mass of unreliable expansion and contractioncharacteristics.

By selecting suitably different graded sizes of chrome particles formaking up the mix and proportioning in the mix the relative quantitiesof the particles of the different selected graded sizes, I obtain a mixthat forms denser, stronger and less porous brick than-are otherwiseobtainable.

In Figure 1, I illustrate a ternary diagram for a series of mixes ofchrome particles having sizes A, B and C. The larger or A particles arethose which are between 10 and 20 mesh per linear inch, the intermediateor B particles will pass 20 mesh per linear inch and be caught on meshper linear inch, while'the smaller or C particles will pass 80 mesh perlinear inch. I

Any point within the diagram represents a-mix having certain definiteproportions'of A, B and C particles, as determined by the perpendiculardistance from that point to the side opposite to the apex of thetriangle indicating of that size of particles. The percentage of A. BandC particles indicated by any point on the diuram total to 100%. Forexample, the point 20 .of Figure 1 corresponds to a mix containing 20%of component A, 30% of component B and 50% of com- I ponent C. Eachcurve on Figure 1 is the locus of mixtures of A, B and C particleshaving the same density. For example, on the curve 21, the chrome brickmade from the mix indicated by the point 22 have the same density as thechrome brick made from the mix indicated-by the point 23, or by anyother point-on that curve. Curve 21 indicates the lowest density mix ofany curve plotted on Figure 1, while curves 24, 25, 26 and 27 indicatemixes which produce chrome brick of increased density, the mix ofgreatest density being that shown by the curve 27. However, the mixindicated by the curve 26 is of very high density.

The areas on the ternary diagram enclosed by the curves of equal densityare progressively smaller as the portion of the diagram for mixes ofhigh density is approached, so that, for high density, there is asmaller range of selection of proportions of various size ranges.

Mixes located within the curve 26 are of high density, and generallyindicate that the percentage of larger or A particles should be between45% and 65%, while the proportion of smaller or C particles should bebetween 35% and 55%, while the intermediate or B particles should beeither eliminated or held to the remaining percentage. The mix ofhighest density should have preferably 55% of larger or A particles and45% of smaller of C particles.

From a practical standpoint, it is more convenient to limit the mix tolarger and smaller particles, that is, to A and C particles, eliminatingthe intermediate or B particles altogether. However, as indicated by'thediagram, a small pro portion of B particles in the mix may have nomaterial tendency to lower the density of the mix and may perhaps evenhave a tendency to raise the density of the mix, provided the proportionis so low that the mix remains in the area of high density. 7

In Figures 3 to 5 inclusive, I have endeavored to indicate on a greatlymagnified scale, different types of granular structure of refractorymixes, the densities of the mixes varying according to the extent towhich the respective grains interfit with one another. It should beunderstood that the contours shown in the figures are not intended torepresent the contours of actual particles, as no attempt has been madeto represent the actual contours of the particles, the figures beingintended merely to indicate a possible reason for the marked changeseffected bymy invention, changes that do take place in the structure ofthe mix and that I have found to give the markedly increased mix densityand markedly better physical characteristic for the brick made from mymix.

In Figure 3, I illustrate a mix made up only of larger chrome grains offairly uniform size, that is, a mix made up only of A particles. Theinterstitial or void spaces 28 between the individual A particles arerelatively few and are considerably reduced in size by reason of thefair interfitting of the individual particles, but are of a content thatis large as compared to that of the idividual C particles, a single voidspace 28 being perhaps large enough to contain many of the C particleswithout changing the relative positions of the adjoining A particles.

In the mix shown in Figure5 the relatively large interstitial spaces 28'between the grains have been filled with small particles C and there hasbeen little change in the relative placement of the large grains, thepresence of the C particles not interfering with the interfitting of theA particles, and, as a result, there has been a material reduction inthe void space as compared to that shown in Figure 3. If the relativeplacement of the A particles be the same as in Figure 3, the presence ofthe small C particles will have reduced the void space by an amountequal to the sum of the volumes of the individual C particles.

A mix represented by the area of high density of Figure 1 might perhapsbe considered to approach or at least tend toward the conditionsindicated in Figure 5, except that the A particles in the actual mixwould probably be more widely variant in size than the A particles ofFigure 5.

and not so large as compared to the C particles of Figure 5.

Figure 4 is intended to represent a mix made up of larger particles A,smaller particles C and particles B of intermediate size. As indicatedin this figure. the particles B of intermediate size interfere with therelative interfitting of the larger particles A and make theinterstitial spaces 28 which may or may not be filled with the Cparticles, larger and more numerous than with the conditions of Figures3 or 5.

It is of course obvious that a different selection of screens may beused in obtaining the A, B and C (larger, intermediate and smaller)grades of particles from that taken for the series of tests representedby Figure 1, and that the position of the equi-density curves will bevariant according to variant selections of these size grading screensand that the focal region representing the relative quantities of A, Band C particles for a mix of maximum density may, to some extent, bevariant with a different selection of grading screens.

The coarseness of the larger particles may be increased to includelarger particles between 3 and 30 mesh per linear inch, while thefineness of the smaller particles may be reduced, using smallerparticles finer than 60 mesh per linear inch or even finer than 80 meshper linear inch. However, good results may be obtained with smallerparticles which pass through 50 mesh per linear inch. I findconsiderable advantage in selecting the A and C particles of decidedlydifferent sizes, so that the belts of larger and smaller particles arenot very close to each other in size} Figure 2 gives a diagrammaticillustration of my method of obtaining a mix made up of larger andsmaller particles without the presence of particles of intermediatesize, as for example, a mix made up of 55% of larger or A particles and45% of smaller or C particles, with substantially no B particles.

The raw material is initially ground and crushed in a mill 29, whichdelivers the ground material at 30 to a course screen 31 which maydesirably be mesh per linear inch, but may permissibly be as large as 3mesh per linear inch.

Any particles too large to pass the screen 31 may desirably be returnedat 32 to the mill 29 for continued grinding.

The material passing the screen 31 drops to a screen 33 of intermediatemesh, for example or mesh per linear inch. The material that fails topass the screen 33 comprises particles of 'the larger or A size, andfalls off the screen 33 into a suitable receptacle or conveyor 34, whilethe material that passes through the screen 33 consists of B orintermediate and C or smaller whence they are delivered at 37 to asecondary grinder 38 which grinds them to the smaller or C size, thegrinder 38 delivering to a screen 39 which is of the same mesh as thescreen 35, and any particles too large to pass this screen beingreturned at 40 to the grinder 38 for continued grinding.

The particles that pass through the screen 35 are the smaller or Cparticles, and drop into a receptacle 41, whence they are taken by asuitable conveyor 42 to a mixer 43. Likewise the particles that pass thescreen 39, which are also smaller or C particles, are delivered from ahopper 44 through conveying means 45 to the conveyor 42, so as to unitethem with the C particles that have passed through the screen 35. Thelarger or A particles from the receptacle 34 are delivered by a conveyor46, partly into the conveyor 42 at 47, and partly into the auxiliarygrinder 38 by a conveyor 48.

In practice the relative quantity of larger or A particles deliveredfrom the mill 29 is readily controlled roughly by suitable adjustment atthe mill 29, but exact adjustment is diflicult and I prefer to operatethe mill 29 to deliver larger or A particles in an indefinite excess ofthe desired quantity, using as much of the A particle material from thescreen 33 to mix .with the C particle material from the screens 35 and39 as is needed for the desired mixture of maximum density, and grindingthe surplus of the larger or A material into smaller or C particles.

When the proper balance is finally obtained,

all of the material leaving the mill 29 is delivered to the mixer 43 inthe desired ratio of larger and smaller sizes, usually of largerparticles to 45% of smaller particles, although the proportion of largerparticles may vary between 45% and and the proportion of smallerparticles may vary between 35% and 55%. Likewise, while the intermediateor B particles are preferably totally absent, they may permissibly bepresent to the extent of between 0 and about 20%. r

I contemplate that conventional brick-making methods will be used, as atpresent applied in chrome brick. I have already explained how thematerial will be ground and the mix made up. Prior to molding the mixwill be suitably moistened, and suitable temporary or permanent bindersmay be incorporated. I will, however, use care to see that suflicientbinder is not added to flux the refractory under furnace conditions. Iwill not add substantial quantities of plastic material to the mix.

The use of high pressure for forming the chrome brick is highlyimportant in my invention, as without it the brick are not desirablydense. I. therefore consider it important in my invention to use for thechrome brick a molding pressure of 1000 pounds per square'inch orgreater. The molding pressure should, however, preferably exceed 5000pounds per square inch, and may exceed 10,000 pounds per square inch.

While my brick may be fired before use, they may desirably be used inunfired condition, relying on the furnace in which the brick areemployed to subject them to firing temperature. In the case of anunfired brick, sodium silicate may be desirably used as a binder. I findthat about 2% of sodium silicate, or even less, will serve as aneffective binder.

Where sodium silicate or any other soluble substance is used as abinder; it will of course be added with water, but the water is not tobe included in the percentage given for the binder.- The percentage isintended to be the proportion of binder in the dry brick.

While I have referred throughout to the use of chrome ore as the rawmaterial for my chrome brick, it will be understood that magnesia(burned magnesite) may be substituted for chrome ore with relativelylittle loss in advan tage. However, I prefer to use less than 50% ofmagnesia in the chrome brick.

The brick subsequent to molding, may either be dried and fired, or theymay be dried and placed in a furnace lining without previous firing.

In either case, the brick will be subjected to firing temperature,whether the firing temperature be that of a kiln or that of the furnacelining or other place in which the brick are ultimately used.

Wherever I refer herein to percentages, I mean percentages by weight,unless the context clearly indicates that percentages by volume areintended, as in the case of porosity.

In view of my invention and disclosure, variations and modifications tomeet individual whim or particular need will doubtless become evident toothers skilled in the art, to obtain all or part of the benefits of myinvention without copying the structure shown, and I, therefore, claimall such in so far as they fall within the reasonable spirit and scopeof my invention.

Having thus described my invention, what I claim as new and desire tosecure by Letters Patent is:

1. A refractory shape of chrome ore and magnesia, comprising between 45%and 65% by weight of larger particles between 3 and 30 mesh per linearinch and between 315% and 55% by weight of smaller particles through 50mesh per linear inch, densely compacted together and adapted to be usedin a furnace lining in unfired condition.

2. The method of making a refractory of high density from non-plasticmaterial preponderantly chrome, and a bonding substance, usingnon-plastic particles of relatively larger and smaller grain sizes,which consists in mixing larger non-plastic particles retained on a 30mesh per linear inch screen with smaller non-plastic particles and abonding substance, while employing not more than a relatively smallproportion of intermediate grain sizes, using a preponderant amount ofchrome in the mix, in molding the mix in moist condition into arefractory shape, in drying the refractory shape and in subjecting thedried unburned refractory shape to firing temperature in a furnacestructure during use. Y

3. The method of making a refractory of high density from non-plasticmaterial preponderantly chrome, and a bonding substance, usingnon-plastic particles of relatively larger and smaller grain sizes,which consists in mixing larger non-plastic particles retained on a 30mesh per linear inch screen with smaller non-plastic particles and abonding substance, while employ ing not more than a relatively smallproportion of intermediate grain sizes, using a preponderant amount ofchrome in the mix, in molding the mix in moist condition under pressureinto a refractory shape, in drying the refractory shape and insubjecting the dried unburned refractory shape to firing temperature ina furnace structure during use.

4. The method of making a refractory of high density from non-plasticmaterial preponderantly chrome, and a bonding substance, usingnon-plastic particles of relatively larger and smaller grain sizes,which consists in mixing larger non-plastic particles retained on a 20mesh per linear inch screen with smaller nonplastic particles and abonding substance, while employing not more than a relatively smallproportion of intermediate grain sizes, using a preponderant amount'ofchrome in the mix, in molding the mix in moist condition under pressureinto a refractory shape, in drying the refractory shape and insubjecting the dried unburned refractory shape to firing temperature ina furnace structure during use. a

,use

5. The method of making a refractory of high density from non-plasticmaterial preponderantly chrome, and a bonding substance, usingnon-plastic particles of relatively larger and smaller grain sizes,which consists in mixing -larger non-plastic particles retained on a 30mesh per linear inch screen with smaller nonplastic particles below 60mesh per linear inch and a bonding substance, while employing not morethan a relatively small proportion of in- 6. The method of making arefractory of high density from non-plastic material, preponder-- antlychrome, and a bond, using non-plastic particles of relatively larger andsmaller grain sizes, which consists in mixing larger non-plasticparticles between 3 and 30 mesh per linear inch in the proportion of 45%to 65% with smaller nonplastic particles below 50 mesh per linear inchin the proportion of 55% to 35%, and with a bond, incorporating apreponderant amount of chrome in the mixture, in molding the mixture inmoist condition under a pressure exceeding 1000 pounds per square inch,in drying the mixture and in subjecting the dried unburned mixture tofiring temperature in a furnace structure during {7. The method ofmaking a refractory of high density from non-plastic materialpreponderantly chrome, and a bond, using non-plastic particles ofrelatively larger and smaller grain sizes, which consists in mixinglarger non-plastic particles between 3 and 30 mesh per linear inch inthe proportion of 45% to 65% with smaller nonplastic particles below 50mesh per linear inch in the proportion of 55% to 35%, and with about 2%of sodium silicate, incorporating a preponderant amount of chrome in themixture, in molding the mixture in moist condition under a pressureexceeding 1000 pounds per square inch, in drying the mixture and insubjecting the dried unburned mixture to firing temperature in a furnacestructure during use.

8. The method of making a refractory of high density from chrome and abonding substance, using larger and smaller grain sizes, which consistsin mixing larger chrome particles retained on a 30 mesh per linear inchscreen with smaller chrome particles and a bonding substance, whileemploying not more than a relatively small proportion of intermediategrain sizes, in molding the mix in moist condition under pressure into arefractory shape, in drying the refractory shape and in subjecting thedried unburned refractory shape to firing temperature in a furnacestructure during use.

9. The method of making a refractory of high density from chrome and abond, using relatively larger and smaller grain sizes, which consists inmixing larger chrome particles between 3 and 30 mesh per linear inch inthe proportion of 45% to 65% with smaller chrome particles below 50 meshper linear inch in the proportion of 55% to 35%, and with a bond, inmolding the mixture in moist condition under a pressure exceeding 1000pounds per square inch, in drying the mixture and in subjecting thedried unfired tureduring use.

10. The method of making a refractory of high density from amixture ofchrome and magnesia containing more chrome than magnesia, and a bondingsubstance, using larger and smaller grain sizes, which consists inmixing together chrome and magnesia particles, with an excess of chrome,using larger particles between 10 and 30 mesh per linear inch withsmaller particles below 60 mesh per linear inch, in roughly equalproportions, and with a bonding substance, in molding the mixture inmoist condition under high pressure, in drying the brick thus formed andin placing the dry unburned brick in a furnace structure.

11. The method of making a refractory of high density from a mixture ofchrome and magnesia containing more chrome than magnesia, and a bond,using relatively larger and smaller grain sizes, which consists inmixing together chromeand magnesia particles with an excess of chrome,using larger particles between 3, and 30 mesh per linear inch in theproportion of 45% to 65% with smaller particles below mesh per linearinch in the proportion of to 35%, and with a bond, in molding themixture in moist condition under pressure exceeding 1000 pounds persquare inch, in drying the mixture and in subjecting the dried unburnedmixture to firing temperature in afurnace structure during use.

12. A dry refractory body preponderantly containing chrome, said bodyhaving low porosity, being in unfired condition and suitable for use inunfired condition, and comprising a densely compacted mixture of largernon-plastic particles capable of being retained on a screen of 30 meshper linear inch-and smaller non-plastic particles capable of passingthrough a screen of mesh per linear inch, in roughly equal proportionsand a bonding substance distributed through the mixture.

13. A dry refractory brick preponderantly containing chrome, said brickhaving low porosity, being in unfired condition and suitable for use inunfired condition, and comprising a densely compacted mixture of aboutequal proportions of larger non-plastic particles between 10 and 30 meshper linear inch and smaller non-plastic particles below 60 mesh perlinear inch and a bond in the mixture.

14. A non-plastic refractory brick preponderantly containing chrome,comprising about 55% of larger non-plastic particles between 10 and 30mesh per linear inch, about 45%, of smaller nonplastic particles below60 mesh per linear inch and a binder, the brick being of requisite coldstrength for use in unfired condition.

15. A dry refractory brick preponderantly containing chrome, said brickhaving low porosity,

being in unfired condition and suitable for usein unfired condition,comprising a densely compacted mixture of between 45% and of largernon-plastic particles between 3 and 30 mesh per linear inch and between55% and 35% of smaller non-plastic particles below 50 mesh per linearinch and a bond in the mixture.

16. A dry refractory brick preponderantly containing chrome, said brickhaving low porosity,

being in unfired condition and suitable for use in unfired condition,comprising a densely compacted mixture of between 45% and 65% of largernon-plastic particles between 3 and 30 mesh per linear inch and between55% and 35% of smaller non-plastic particles below 50 mesh per linearinch and about 2% of sodium silicate in the mixture.

17. A dry chrome brick having low porosity,.

being in unfired condition and suitable for use in unfired condition,comprising a densely compacted mixture of between 45% and 65% of largernon-plastic particles between 3 and 30 mesh per linear inch and between55% and 35% of smaller non-plastic particles below 50 mesh per linearinch and a bond in the mixture.

18. A dry chrome-magnesia brick containing more chrome than magnesia,having low porosity, being in unfired condition and suitable for use inunfired condition, comprising a densely compacted mixture of between 45%and 65% of larger non-plastic particles between 3 and 30 mesh per linearinch and between 55% and 35% of smaller non-plastic particles below 50mesh per linear inch and a bond in the mixture.

RUSSELL PEARCE

